The present invention relates, in general terms, to a control linkage for a driven component which has a substantially linear travel, in which a lever comprises, on respective sides of an axis of rotation, a first arm subjected to the action of a control element and a second arm acting on the driven component. The invention applies especially to the control levers of clutch bearings, commonly known as forks, and the following description refers to such uses. However, it must be remembered that this is an important, but not exclusive use of the invention.
Clutch forks known at the present time assume somewhat varied forms. However, they can be described in general terms as levers which comprise, on respective sides of an axis of rotation, in particular a knuckle connected to a fixed frame, a first arm subjected to the action of a control element, actuated, for example, by the clutch pedal of a motor vehicle, and a second arm acting on a clutch bearing. The abovementioned knuckle performs a double function: it constitutes an axis of articulation for the fork, whilst ensuring that it is supported.
As is known, a clutch bearing is intended to act, by pushing (pushed bearing) or by pulling (pulled bearing), on the disengaging device of a clutch, for example, a diaphragm. In the position of rest within a clutch, this disengaging device presses a pressure plate in the direction of a reaction plate, both being fixed in rotation to a drive shaft, thus ensuring the rotational drive of a friction disc interposed between the two plates and fixed to a driven shaft, in practice the input shaft in a gearbox. When it is actuated by the bearing, the device releases the pressure of the pressure plate on the disc, thus allowing the latter to disengage from the plates. As is known, the quality of this disengagement depends greatly on the accuracy with which the bearing is aligned with the diaphragm and therefore the clutch as a whole. Consequently, the manufacturers seek to ensure that the bearing follows as straight and as accurate a path as possible in alignment with the axis of the associated clutch.
They first proposed to have the bearings supported by the associated forks. Such a bearing, called a supported bearing, generally has for this purpose two diametrically opposite journals rotating in bearings fastened to two projections or fingers of the fork. As a result of the method of fastening the latter, the clutch bearing has a path in the form of an arc of a circle, thus leading to a variable radial movement between the bearing and the diaphragm and consequently to wearing of their surfaces in contact.
To mitigate this disadvantage, it was proposed to use bearings, called guided bearings, mounted to slide along a guide tube, commonly called a shaft casing, surrounding the input shaft of a gearbox, or directly on the said shaft. The free end of such a shaft is conventionally mounted in a bearing carried by the drive shaft. In order to reduce the cost and the assembly time, the manufacturers then aimed at eliminating this bearing.
However, the overhung mounting of the input shaft resulted in an increase in the diameter of the latter and therefore an increase in the diameter of the guide tube to the detriment of the cost price.
The applicant also proposed to mount a clutch bearing to slide along two small columns (French Patent Application No. 7,639,540) parallel to the axis of the clutch, but offset. However, the best possible guidance of such a bearing, together with minimum wear, requires a strict parallel alignment of the said columns.
Moreover, in general, because the guided bearings are actuated under the action of pivoting forks of the type mentioned above, wear arises between the contact surfaces of the fork and of the bearing as a function of the position of the axis of rotation of the fork.
The present invention aims to mitigate these disadvantages, whilst ensuring that the bearing zones of the fork have a substantially rectilinear movement and whilst eliminating as far as possible all the sources of wear in respect of the suspension of the fork and its contact with the bearing.